1. Field of the Invention
The present invention relates to a device for monitoring the superplastic forming of a metallic piece from a blank positioned at the entrance of a mold charged by compressed gas.
2. Description of the Prior Art
The superplastic forming of metals has been known for several years (see, for example, French Pat. No. 1,495,606). It allows deep shapes to be formed which could not be made in any other way without damaging the metal. It is thus possible to make rough models with a minimum mass, which considerably reduces the machining time necessary to manufacture the finished piece.
Nevertheless, in this forming process, as the metal is being stretched, the thickness of the blank decreases, the deformation rate tends to increase to the extent that critical values are reached which could be detrimental to the quality of the part.
U.S. Pat. Nos. 3,934,440 and 4,011,744, as well as Australian Pat. No. 115,957, teach that these disadvantages can be eliminated by using a device for monitoring the forming step, the device being of the type which has a rigid sliding element for measuring the movement of the central part of the blank. One end of the sliding element rests on the central part of the blank and can slide when the central part of the blank moves. Associated with the sliding element is a system for measuring the movement of the element. The term "central part of the blank" designates the part which deforms the most rapidly, because it is the furthest-removed from the walls of the molds. Although generally located at the center of the blank, this part can nevertheless be positioned away from the center, depending on the exact shape of the mold.